1. Field of the Invention
The present invention relates to an engine control unit, and more particular, to a control unit that controls a combustion system for vehicular internal combustion engines, in which a combustion system such as spark ignition combustion, compression ignition combustion, etc. can be switched over.
2. Description of Related Art
Among internal combustion engines (referred below to engine) used for automobiles, etc., attention has been paid to a compression ignition type gasoline engine (referred below to as compression ignition engine), which compresses a mixture to cause self ignition combustion (referred below to as compression ignition combustion) and makes an improvement in fuel consumption performance and an improvement in exhaust performance compatible with each other.
A compression ignition engine that performs compression ignition combustion (first combustion system) can realize making fuel consumption performance and exhaust performance compatible with each other since high efficiency by high compression and lean combustion reduce fuel consumption to exhibit an excellent fuel economy and low temperature combustion of a mixture reduces emission of NOx as compared with a spark ignition engine, in which sparks from an ignition plug ignite and burns a mixture.
Compression ignition combustion in gasoline engines can be materialized in low load-low engine speed. Therefore, compression ignition engines make it necessary to carry out compression ignition combustion and spark ignition combustion (second combustion system) and to switch over between the combustion modes.
Switchover of compression in the related art is carried out judging whether switchover is possible, on the basis of a map decided by engine load and engine speed (for example, JP-A-2003-201876 and JP-A-2004-27959).
Also, in addition to the map of engine load and engine speed, in order to prevent combustion from becoming unstable in sensing emergency braking, it has been proposed to switch over between combustion modes from compression ignition combustion to spark ignition combustion (for example, JP-A-2004-11539).
That is, switchover of compression in the related art is mainly judged on the basis of an operating state of an engine.
However, safety performance and operational performance are not ensured in some vehicles, to which the related art is applied. The reason for this is that switchover between combustion modes, which is optimum for a vehicle, cannot be realized in some cases since switchover between compression ignition combustion and spark ignition combustion is judged.carried out on the basis of an operating state of an engine.
Under, for example, an operating condition that acceleration is frequently carried out in that range of engine load, in which compression ignition combustion is made possible, by virtue of an output of compression ignition combustion being low in responsibility, response to a demanded load cannot be in some cases realized to ensure an operational performance.
Also, likewise, by virtue of an output of compression ignition combustion being low in responsibility, a demand for engine load from a control unit for improvement of a vehicle in stability cannot be in some cases realized to ensure a safety performance of a vehicle.